On the Formation of Phantom Electron Phase Space Density Peaks in Single
Spacecraft Radiation Belt Data
Abstract
This paper examines the rapid losses and acceleration of trapped
relativistic and ultrarelativistic electron populations in the Van Allen
radiation belt during the September 7-9, 2017, geomagnetic storm. By
analyzing the dynamics of the last closed drift shell (LCDS) and the
electron flux and phase space density (PSD), we show that the electron
dropouts are consistent with magnetopause shadowing and outward radial
diffusion to the compressed LCDS. During the recovery phase, an in-bound
pass of Van Allen Probe A shows an apparent local peak in PSD. However,
a fortuitous timing of a crossing of the two Van Allen Probes reveals
instead how the apparent PSD peak arises from aliasing monotonic PSD
profiles which are rapidly increasing due to acceleration from very fast
inwards radial diffusion. In the absence of such multi-satellite
conjunctions during fast acceleration events, the source might otherwise
be attributed to local acceleration processes.